Ultrabright Fluorescent and Lasing Microspheres from a Conjugated Polymer

Abstract Fluorescent microspheres are used for biomarkers, assay substrates, chemical diagnostics, flow cytometry, and biological imaging. These applications demand the highest fluorescence intensity achievable; however, concentration quenching limits the amount of dye that can be practically incorporated in conventional fluorescent microspheres. Conjugated polymers (CPs) can be less susceptible to concentration quenching, suggesting that they can be excellent candidates for a new class of light‐emitting microspheres. Due to their long‐chain‐conjugated backbone, however, CPs can be resistant to forming smoothly curved or spherical structures. Here, strongly fluorescent CP microspheres as large as 100 µm in diameter are synthesized. Whispering gallery modes (WGMs) appear in the fluorescence spectra, and the microspheres show clear evidence of lasing above a threshold pump intensity. These conjugated polymer beads are up to 50 times larger than CP microspheres obtained by other methods, and they exceed the emission intensity of conventional fluorescent microspheres by more than an order of magnitude.